National Centre for Scientific Research
"Demokritos", Institute of Materials Science

Athens, Greece

Synthesis of Iron(II) acetate
hydrate (ferrous acetate)

Pure and soluble iron(II) acetate hydrate,
which can be useful in synthesis of ferrous complexes, is prepared by
oxidation of metallic iron in acetic acid. Anhydrous iron(II) acetate is
very insoluble and less useful for synthetic purposes. In addition, when
certain types of spectroscopy are envisaged, high-purity iron(II)
acetate is required. In particular, ferric impurities will show up in
EPR spectra even at trace amounts (iron(III) is a Kramers ion), while
iron(II) (a non-Kramers ion) gives much weaker EPR signals (if at all).

Assemble the two 0.5 L flask on the two sides of the Schlenk frit as
shown in Figure 1.

Use two stirring magnets (the second will
be used after the apparatus has been inversed) and protect the frit
pores from clogging with unreacted iron powder using glasswool. Stopper
the second neck of the bottom flask with a rubber septum.

2.

Add 25 g of metallic iron powder to the
bottom flask and purge the whole setup by 4-5 vacuum-nitrogen cycles.

3.

Deoxygenate in a separate Schlenk flask 90
ml of acetic acid and decanulate it through the rubber septum.
Similarly, decanulate 90 mL of deoxygenated distilled H2O
into you setup.

4.

A small evolution of H2 will
commence as the metallic iron is oxidised by water. Open the top valve
to an oil bubbler and maintain a small nitrogen flow to impede air from
entering.

Allow ~1 hr for this reaction to proceed
at this rate.

5.

Immerse the setup in an oil bath (or use a
heating mantle if available) and heat to reflux (~115 oC).
Make sure to tilt your setup so that the refluxing solvents do not pass
over the stopcock valves. Continue the reflux for ~6-8 hr.

6.

At the end of this period, most of the
iron has reacted, but usually not all. Remove from heating and allow to
cool.

When the mixture is still warm inverse the
apparatus to filter. Use stopcock (C) to evacuate the apparatus and (A)
to pressurize with nitrogen in order to accelerate the filtration. The
solution should be a pale green color.

7.

When the filtration is complete, stop the
inflow of nitrogen and open all stopcocks to vacuum (first, (C), then
(B), then (A)). The solvents will start evaporating and condense in the
cold trap.

8.

When this is complete, a white foam will
form. Close all stopcocks and while under vacuum, enter the apparatus
into the glovebox (if the apparatus is not under vacuum, it may explode
inside the antechamber).

9.

Scrape the foam off the flask walls and
grind it in a mortar. Return to the flask, add dry acetone and agitate.
Filter on a Buchner funnel. The first filtrate should be light brown.
Repeat the washing with dry acetone 2-3 times. The rest of the filtrates
should be pale green or colorless.

10.

Vacuum dry and store in tightly sealed
vials.

The dried material should
be white, with only a hint of green.

The material should be checked for its
purity. Apart from microanalyses that would determine its degree of
hydration (normally ~2 H2O solvates are expected per formula
unit), X-band EPR spectroscopy is very useful in determining other
impurities. Common impurities are:-monomeric iron(III) (rhombic g ~ 4.3
signal in the EPR spectrum)-monomeric Mn(II) impurities (g ~ 2.0 sextet
in the EPR spectrum)These can be detected by X-band EPR
spectroscopy to levels below 1%.

EPR spectra of iron(II) acetate
prepared from 97% metallic iron, might show trace manganese impurities before
washing with dry acetone (depending on the quality of metallic iron). However, these totally disappear after 3
washings. The EPR spectra should also be totally free of ferric
impurities if all manipulations were well carried out. In the examples
below, after the washings, only the EPR cavity is visible at 300 K.

Before washing

After washing

On the other hand, manganese impurities
may not show up at all, even in the "impure" material (prior to
washing).